1. Field of the Invention
This invention relates to methods and apparatuses for modifying intervertebral disc tissue and more particularly to the treatment of annular fissures and disc defects using percutaneous techniques to avoid major surgical intervention.
2. Description of Related Art
Intervertebral disc abnormalities have a high incidence in the population and may result in pain and discomfort if they impinge on or irritate nerves. Disc abnormalities may be the result of trauma, repetitive use, metabolic disorders and the aging process and include such disorders but are not limited to degenerative discs (I) localized tears or fissures in the annulus fibrosus, (ii) localized disc herniations with contained or escaped extrusions, and (iii) chronic, circumferential bulging discs.
Disc fissures occur rather easily after structural degeneration of fibrous components of the annulus fibrosus during a part of the normal aging process that may be accelerated by trauma. Sneezing, bending or just attrition can tear these degenerated annulus fibrosus fibers, creating a fissure. The fissure may or may not be accompanied by extrusion of nucleus pulposus material into or beyond the annulus fibrosus. The fissure itself may be the sole morphological change, above and beyond generalized degenerative changes in the connective tissue of the disc. Even if there is no visible extrusion, biochemicals within the disc may leak out of the contained intervertebral disk and irritate surrounding structures. Disc fissures can also be debilitatingly painful. Initial treatment is symptomatic, including bed rest, pain killers and muscle relaxants. More recently, spinal fusion with cages have been performed when conservative treatment did not relieve the pain. The fissure may also be associated with a herniation of that portion of the annulus.
With a contained disc herniation, there are no free nucleus fragments in the spinal canal. Nevertheless, even a contained disc herniation is problematic because the outward protrusion can press on the spinal nerves or irritate other structures such as the corresponding nerve root. In addition to nerve root compression, escaped nucleus pulposus contents may chemically irritate neural structures. Current treatment methods include reduction of pressure on the annulus by removing some of the interior nucleus pulposus material by percutaneous nuclectomy. However, complications include disc space infection, nerve root injury, hematoma formation, instability of the adjacent vertebrae and collapse of the disc from a decrease in height.
Another disc problem occurs when the disc bulges outward circumferentially in all directions and not just in one location. Overtime, the disc weakens and takes on a “roll” shape or circumferential bulge. Mechanical stiffness of the joint is reduced and the joint and spinal column may become unstable. One vertebrae may settle on top of another. This problem continues as the body ages and accounts for a shortened stature in old age. With the increasing life expectancy of the population, such degenerative disc disease and impairment of nerve function are becoming major public health problems. As the disc “roll” extends beyond the normal circumference, the disc height may be compromised, foramina with nerve roots becomes compressed. In addition, osteophytes may form on the outer surface of the disc roll and further encroach on the spinal canal and foramina through which nerves pass. This condition is called lumbar spondylosis.
It has been thought that such disc degeneration creates segmental instability which disturbs sensitive structures which in turn register pain. Traditional, conservative methods of treatment include bed rest, pain medication, physical therapy or steroidal injections. Upon failure of conservative therapy, spinal pain (assumed to be due to instability) has been treated by spinal fusion, with or without instrumentation, which causes the vertebrae above and below the disc to grow solidly together and form a single, solid piece of bone. The procedure is carried out with or without discectomy. Other treatments include discectomy alone or disc decompression with or without fusion. Nuclectomy can be performed by removing some of the nucleus to reduce pressure on the annulus. However, complications include disc space infection, nerve root injury, hematoma formation, and instability of adjacent vertebrae.
These interventions have been problematic in that alleviation of back pain is unpredictable even if surgery appears successful. In attempts to overcome these difficulties, new fixation devices have been introduced into the market, including but not limited to pedicle screws and interbody fusion cages. Although pedicle screws provide a high fusion success rate, there is still no direct correlation between fusion success and patient improvement in function and pain. Studies on fusion have demonstrated success rates of between 50% and 67% for pain improvement, and a significant number of patients have more pain postoperatively. Therefore, different methods of helping patients with degenerative disc problems need to be explored.
FIGS. 1A and 1B illustrate a cross-sectional anatomical view of a vertebra and associated disc and a lateral view of a portion of a lumbar and thoracic spine, respectively.
Structures of a typical cervical vertebra (superior aspect) are shown in FIG. 1A: 104—lamina; 106—spinal cord; 108—dorsal root of the spinal nerve; 114—ventral root of the spinal nerve; 116—posterior longitudinal ligament; 118—intervertebral disc; 120—nucleus pulposus; 122—annulus fibrosus; 123—anterior longitudinal ligament; 126—vertebral body; 128—pedicle; 130—vertebral artery; 132—vertebral veins; 134—superior articular facet; 136—posterior lateral portion of the annulus; 138—posterior medial portion of the annulus; and 149—spinous process. In FIG. 1A, one side of the intervertebral disc 118 is not shown so that the anterior vertebral body 126 can be seen. FIG. 1B is a lateral aspect of the lower portion of a typical spinal column showing the entire lumbar region and part of the thoracic region and displaying the following structures: 118—intervertebral disc; 126—vertebral body; 142—spinous process; 170—inferior vertebral notch; 110—spinal nerve; 174—superior articular process; 176—lumbar curvature; and 180—sacrum.
The presence of the spinal cord and the posterior portion of the vertebral body, including the spinous process, and superior and inferior articular processes, prohibit introduction of a needle or trocar from a directly posterior position. This is important because the posterior disc wall is the site of symptomatic annulus tears and disc protrusions/extrusions that compress or irritate spinal nerves for most degenerative disc syndromes. The inferior articular process along with the pedicle and the lumbar spinal nerve, form a small “triangular” window through which introduction can be achieved from a posterior lateral approach. FIG. 1D is an overhead view of an instrument introduced by the posterior lateral approach. It is well known to those skilled in the art that percutaneous access to the disc is achieved by placing an introducer into the disc from this posterior lateral approach, but the triangular window does not allow much room to maneuver. Once the introducer pierces the tough annulus fibrosus, the introducer is fixed at two points along its length and has very little freedom of movement. Thus, this approach has allowed access only to small central and anterior portion of the nucleus pulposus. Current methods do not permit percutaneous access to the posterior half of the nucleus or to the posterior wall of the disc. Major and potentially dangerous surgery is required to access these areas.
Accordingly, these problems with spinal column surgery have been addressed by Applicants in U.S. Pat. Nos. 5,980,504, 6,007,570, U.S. application Ser. No. 09/363,824, filed Jul. 30, 1999, U.S. application Ser. No. 09/236,816 filed Jan. 25, 1999, U.S. application Ser. No. 09/162,704 filed Sep. 29, 1998, U.S. application Ser. No. 09/153,552 filed Sep. 15, 1998 and U.S. application Ser. Nos. 08/881,525, 08/881,692, 08/881,694, all filed Jun. 24, 1997, which are incorporated by reference
Accordingly, it is desirable to provide an improved access apparatus and method by which the interior nucleus of an intervertebral disc may be accessed and annular fissures or herniations can be treated or repaired. It would be further desirable to provide a modular exchange system to address various functions such as delivery of energy, delivery of medicaments, removal of material or providing access for physical and chemical modification of the nucleus and annulus.